Steam generator system

ABSTRACT

A forced-circulation, once-through steam generator for secondary oil recovery passes flue gases through a spray tower to heat feed water for a lime and soda ash softening treatment by upflow through a sludge blanket.

United States Patent [72] Inventor Cornelis Hoogendlm 50] Field of Search 210/56, Houston, Tex. 198; 122/1, 4, 379 [21 Appl. No. 850,507 [22] Filed Aug. 15, 1969 [56] References Clted [45] Patented Feb. 16, 1971 UNITED STATES PATENTS 1 5 8? Smith's 1 2,937,624 5/1960 Brogdon, Jr. 122/1 Prwmy s- 20, 1963 3,041 ,274 6/1962 Love et al. 210/56 1 3,125,072 3/1964 Brandt et a1. 122/4 ,806/68 Primary Exammer-Kenneth W. Sprague Attorney-William A. Drucker 1 [54] STEAM GENERATOR SYSTEM 6 Claims 1 Drawing ABSTRACT: A forced-circulation, once-through steam [52] US. Cl 122/1, generator for secondary oil recovery passes flue gases through 6 122/379 a spray tower to heat feed water for a Mime and soda ash sof- [SI 1 Int. ("I F22]: 37/48 tening treatment by upflow through a sludge blanket.

Pm fd' Feb. '16, 1911 MM M \m mm 0 a 1 STEAM GENERATOR SYSTEM BACKGROUND OF THE INVENTION Steam generators for secondary oil recovery should produce steam at at least 80 percent quality to be injected into the well. This steam reduces the viscosity of heavy crude oil and improves its pumpability. The best type of steam generator for this purpose is of a forced-circulation, once-through design which is very unlike a conventional steam boiler.

This type of steam generator is unique in that it will handle a relatively high percentage of solids, provided the solids have been converted to a soluble form. This type of steam generator does not have a separating drum and is essentially only a once-through heated pipe coil. Thus, this type of steam generator, because it has a small volume of water and steam in the coil and because it lacks a separating drum, does not conform to the classic definition of a steam boiler. For these reasons, a steam generator system of the once-through type must include adequate feed water treatment means.

Themain hardness to be treated in the feed water is the presence of calcium carbonate. (CaCO and magnesium hydroxide (Mg(OI-l) Since 80 to 85 percent of the feed water is vaporized in the single pass through the steam generator, it is absolutely essential to have zero hardness in the feed water at all times.

It has been conventional to use the dual ion-exchange system to provide minimum hardness leakage even with difficult raw waters. Most of the time hardness sequestering agents are used as an added safety factor. However, the sodium zeolite softening process has some severe limitations in that hardness is removed without any reduction in alkalinity or total dissolved solids, very turbid waters and waters containing oil will foul the resin bed and cause many operating problems, and if the sodium chloride content goes over 4,000 ppm, the softener becomes very uneconomical to operate and residual hardness will be quite high. T i

In areas where steamflooding is used successfully, it is becoming increasingly hard to find feed waters that can be softened by the ion-exchange process. When oil is pumped out of the ground, a certain percentage of water is also pumped up. This water has to be separated frornthe oil and disposed of. With antipollution laws coming into effect, it is becoming increasingly hard to dispose of this waste water. This invention allows the economical use of this waste water in a steam generator system.

SUMMARY OF THE INVENTION BRIEF DESCRIPTION OF THE DRAWING The FIG. is a schematic flow diagram of the system of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT A steam generator 30 contains coils 31 which are heated by an oil burner or the like 32. A flue 34 from generator 30 con tains coils 33 to preheat feed water pumped from steam generator feed pump 35 through line 36. Steam discharge line 37 leads to a well (not shown) for steam injection.

The spray tower 38 is a cylindrical or square tank 40 with a storage area 39 at its bottom. Tank 40 has a flue gas inlet 41 in a lower side i with a water shed 42 extending outward thereover. Three rows of nozzles 6 on pipes, 45, and 46 branching from a common manifold 47 and controlled by valves 48, 49, and 50, are disposed in the upper part of tank 40. The nozzles 6 are directed upward and all feed water has to pass through these nozzles 6. A mist eliminator 7 disposed at the top of tank prevents vapor loss to the atmosphere. The flue gas flows upward contacting and heating feed water to about 200 F. as it falls into the storage section 39.

The spray tower 38 increases the eff ciency of combustion of the steam generator 30 because the temperature of flue gases leaving the mist eliminator 7 is about 120 F. It would take a lot of convention surface to achieve a 120 F. flue gas temperature and such surface would be very costly. With the spray tower 38, the water of combustion is condensed and part of this heat of condensation is recovered. A 10 percent increase in efficiency based on L.V.H. can be obtained by this condensation alone. The combined efficiency increase by recovering the latent heat of condensation and the lowering of stack temperature will be about 10 percent to 15 percent based on L.V.I-l. This increase in efficiency will lower the cost of water produced by about $0.01 per barrel. It is to be noted that waste heat recovered to soften water is mostly conserved and increases the temperature of feed water entering pump Referring further to the FIG., raw water 50 is pumped by pump 51 from a pond or the like from below an oil skimmer 52 through line 53. This raw water may be passed through an oil filter 54 if required and then through the level control valve 4 which is remotely controlled by level-detecting apparatus 8. The water then enters manifold 47 to spray into tower 38. It is to be noted that the system of this invention can operate with some slight amounts of oil in the feed water reaching spray tower 38.

As has been explained, the feed water is heated by flue gas within spray tower 38. This heated water falls on the perforated division plate 56 which serves to prevent the absorption of CO in the very alkaline water surface in reaction chamber 57. In the conically shaped chamber 57, lime and soda ash are introduced through the pipes 59 and 60 to be thoroughly mixed with the feed water.

These chemicals quickly react with the hardness-forming constituents at the elevated temperature to precipitate these as calcium carbonate and magnesium hydroxide. Thus the water is softened according to the following reactions:

Ca( HCO Ca(Ol-lh 2CaCO 2H O Mg(I-ICO +2Ca(Ol-I) Mg(0ll]1 2CaCO 2I-I,O Other reactions take place, but these are not detrimental to the reduction of hardness or to the usage of treated water in a steam generating system according to this invention.

The hot softened water with its precipitates flows down through the inner funnel 61 into takedown pipe 61 from which it emerges in the conical bottom 62 of reaction chamber 57. The feed filters upward through a suspended blanket 63 of previously formed precipitates. This filtration removes any small particles of sludge which might otherwise carry over into the feed. Emerging from the top of the sludge blanket 63, the feed moves to collector system 64 and through pipe 65 and pump 2 to the filters 22,22 and 22".

' To effect a better usage of chemicals, the sludge in blanket 63 is recirculated through one of the lines 66-72, pump 3, and line 73. Some of the sludge and solids are continuously discharged through line 74 and ejector 21 to sludge pit 75. A

quick-opening value 20 is used with ejector 21 to remove slugs of solids which could form in the bottom of chamber 57 with the limited head of pressure that is available. a

The feed passes through line 65 to the filters 22, 22, and 22"where it is continuously filtered through anthracite.

\ Backwashing is accomplished with hot water from line 65 which is drawn through valve 79 and line 80 by backwash pump 1. Backwash from the filters returns through line SI to spray tank 40. With three filters in the system, very little upset will occur.

Lime from hopper l2 and dissolver III is passed by pump 13 through line 83, valve 10 and check valve 15 into chamber 47.

Soda ash mixed in tank 23 is passed by pump 26 through line 84 to enter the chamber 57.

Specific valving, feedlines, return lines, level controls, etc. are indicated on the drawing and will be obvious to those skilled in the chemical arts.

From the foregoing description, it may be seen that the steam-generating system of this invention combines a direct contact spray tower heat economizer with a hot process softening system. This system is compact, saves fuel, is inexpensive' to construct, requires no pressure vessel, reduces the solids content of the feed water, and minimizes the pollution problem.

In testing the apparatus of this invention, it was found that the spray tower 38 had the added advantage of reducing the H 8 28 content of feed water. Water was successfully produced at zero hardness at a cost of less than 1.2 cents per barrel.

While this invention has been shown and described in the best form known, it will nevertheless be understood that this is purely exemplary and that modifications may be made without departing from the spirit and scope of the invention.

lclaim:

l. A steam generator system for secondary oil recovery comprising, in combination, water-heating coils, combustion means heating said coils having a flue conducting products of combustion therefrom, a spray tower containing a lower water storage area and upper water spraying nozzles, said flue conducting at least some of said products of combustion into said spray tower above said storage area to rise in said spray tower and heat water sprayed from said nozzles to provide hot water in said storage area, a conical reaction chamber, means introducing lime and soda ash into hot water from said storage area, means introducing the hot water containing lime and soda ash into the bottom of said reaction chamber, a suspended sludge blanket formed by precipitates in said reaction chamber through which water passes upward to be treated, means drawing treated water from said reaction chamber above said sludge blanket, and means forcing the treated water through said heated coils in one pass producing steam for secondary oil recovery.

2. The combination according to claim 1 wherein said conical reaction chamber is disposed directly below said storage area of said spray tower; wherein said means introducing the hot water containing lime and soda ash into the bottom of said reaction chamber comprises an inner funnel and takedown pipe within said reaction chamber below said storage area, said takedown pipe leading to the bottom of said reaction chamber; and with the addition of a division plate between said storage area and said inner funnel, said means introducing lime and soda ash into said inner funnel.

3. The combination according to claim 2 with the addition of a sludge recirculation loop comprising at least one first drawing sludge into said first pipe, and a second pipe through which said pump recirculates sludge into said inner funnel.

4. The combination according to claim 3 with the addition of a quick-opening valve and an ejector connected to the bottom of said reaction chamber removing slugs of solids therefrom.

5. The combination according to claim 4 with the addition of fluid level responsive means responding to the water level in said storage area, valve means regulating the flow of water to said nozzles in said spray tower, and control means activated by said fluid level responsive control means regulating said valve means.

6. The combination according to claim 5 with the addition of a storage tank holding treated water from said reaction chamber before said treated water is forced through said heated coils, said storage coils allowing startup of the steam generator system. 

1. A steam generator system for secondary oil recovery comprising, in combination, water-heating coils, combustion means heating said coils having a flue conducting products of combustion therefrom, a spray tower containing a lower water storage area and upper water spraying nozzles, said flue conducting at least some of said products of combustion into said spray tower above said storage area to rise in said spray tower and heat water sprayed from said nozzles to provide hot water in said storage area, a conical reaction chamber, means introducing lime and soda ash into hot water from said storage area, means introducing the hot water containing lime and soda ash into the bottom of said reaction chamber, a suspended sludge blanket formed by precipitates in said reaction chamber through which water passes upward to be treated, means drawing treated water from said reaction chamber above said sludge blanket, and means forcing the treated water through said heated coils in one pass producing steam for secondary oil recovery.
 2. The combination according to claim 1 wherein said conical reaction chamber is disposed directly below said storage area of said spray tower; wherein said means introducing the hot water containing lime and soda ash into the bottom of said reaction chamber comprises an inner funnel and takedown pipe within said reaction chamber below said storage area, said takedown pipe leading to the bottom of said reaction chamber; and with the addition of a division plate between said storage area and said inner funnel, said means introducing lime and soda ash into said inner funnel.
 3. The combination according to claim 2 with the addition of a sludge recirculation loop comprising at least one first drawing sludge into said first pipe, and a second pipe through which said pump recirculates sludge into said inner funnel.
 4. The combination according to claim 3 with the addition of a quick-opening valve and an ejector connected to the bottom of said reaction chamber removing slugs of solids therefrom.
 5. The combination according to claim 4 with the addition of fluid level responsive means responding to the water level in said storage area, valve means regulating the flow of water to said nozzles in said spray tower, and control means activated by said fluid level responsive control means regulating said valve means.
 6. The combination according to claim 5 with the addition of a storage tank holding treated water from said reaction chamber before said treated water is forced through said heated coils, said storage coils allowing startup of the steam generator system. 